1. Field of the Invention
This invention relates to a chlorine-containing resin composition which is non-toxic or of low toxicity and which has excellent thermal stability for long periods of time.
2. Description of the Prior Art
It is necessary to incorporate a thermal stabilizer into chlorine-containing resins upon processing. The main thermal stabilizers which have been conventionally used for stabilizing chlorine-containing resins include inorganic acid salts, organic acid salts, organic tin compounds and the like and, particularly among these conventional stabilizers, lead salts and lead soaps are widely employed due to their excellent thermal resistance effects and low cost.
Many of these stabilizers are toxic, e.g., those containing lead, and accordingly their utility is limited. On the other hand, calcium-containing stabilizers have recently come into popular use as a non-toxic or of low toxicity stabilizer. The calcium-containing stabilizers include calcium hydroxide, calcium carbonate and the like. However, although calcium hydroxide has a high ability to scavenge free hydrogen chloride which is evolved during the thermal decomposition of the chlorine-containing resins, hydrogen chloride is also taken out from the resin molecules upon molding due to the high basicity of the calcium hydroxide, accelerating deterioration and coloring the resins. Further, in the case of using calcium carbonate as a stabilizer, since its ability to scavenge hydrogen chloride is weak, free hydrogen chloride which is evolved during the decomposition of the chlorine-containing resins is not sufficiently scavenged, thereby accelerating decomposition and coloring of the chlorine-containing resins.